Clear Air Turbulence Caused by Storm Top Internal Gravity Wave Breaking Based on Satellite Data

Many observational studies indicate that clear air turbulence (CAT) phenomenon, which poses serious aviation hazard, is closely associated with deep convective storms. Hence it is desirable to understand how such storms generate CAT and how CAT spreads in time. Moreover, it will be highly beneficial if a forecast technique can be developed based on satellite data, especially those from the geosynchronous satellites, so that storm activity can be monitored continuously.

                Recently a few satellite-observed cloud top features of some severe storms in both visible and infrared channels have been identified. These include enhanced-V (cold-V), warm-cold couplet, above anvil plumes and jumping cirrus. In order to understand the physical mechanisms responsible for producing these feature, we conducted cloud model simulation studies and showed that all these features are basically the result of the interaction between the strong updraft due to the deep convection and the ambient winds. The updraft produces vigorous internal gravity waves which breaks under suitable interaction condition with the ambient wind. The wave breaking is mainly responsible for CAT. With this main understanding, it is now possible to come up with a unified theory how all such features occur and how they are related to CAT. Such an understanding will be beneficial to CAT forecast.

                In the present paper, we will report on the observed phenomena and use model simulation to illustrate the physical mechanisms responsible for their generation. We will also show that these phenomena are all interrelated and can be used an indicators of CAT potential.